1.1 The Origin of Microorganisms

Theory of Spontaneous Generation Revisited

1. The experiments of Pasteur refuted the theory of spontaneous generation. (Figure 1.2)

2. The experiments of Tyndall and Cohn demonstrated the existence of heat-resistant forms of bacteria that could account for the growth of bacteria in infusions that had been heated.

The First Microorganisms (Figure 1.1)

1. The progenitors of microorganisms no longer exist, but it seems likely that the first microorganisms probably grew in the absence of air and at very high temperatures. These were the conditions of the early earth.

1.2 Microbiology: A Human Perspective

Vital Activities of Microorganisms

1. The activities of microorganisms are vital for the survival of all other organisms, including humans.

2. Bacteria are necessary to convert the nitrogen gas in air into a form that plants and other organisms can use.

3. Microorganisms replenish the oxygen on earth.

4. Microorganisms degrade organic waste materials.

Applications of Microbiology

1. For thousands of years, bread, wine, beer, and cheeses have been made by using technology still applied today.

2. Bacteria are being used to degrade dangerous toxic pollutants.

3. Bacteria are used to synthesize a variety of different products, such as cellulose, hydroxybutyric acid, ethanol, antibiotics, and amino acids.

Genetic Engineering

1. Genetic engineering is the process in which genes from one organism are introduced into related or unrelated organisms resulting in new properties.

2. Genetic engineering has expanded the capabilities of microorganisms enormously.

3. Microorganisms produce medically important products and can produce vaccines against a variety of diseases.

4. A bacterium can transfer genes into plants and modify their properties.

Medical Microbiology

1. Many devastating diseases such as smallpox, bubonic plague, and influenza have determined the course of history.

2. "New" emerging diseases are arising in developed countries. Partly, this is because people are engaging in different lifestyles and living in regions where formerly only animals lived. (Figure 1.3)

3. "Old" diseases that were on the wane have begun to reemerge. Many are brought to this country by people visiting foreign lands.

4. Several chronic diseases such as ulcers and perhaps even heart disease may be caused by bacteria.

5. Bacteria use the body as an ecological habitat and interact with other bacteria on its surface. Pathogens gain entrance to the body and find a protected habitat inside host cells.

Microoganisms As Subjects for Study

1. Microorganisms are excellent model organisms to study because they grow rapidly on simple, inexpensive media, but follow the same genetic, metabolic, and biochemical principles as higher organisms.

1.3 The Microbial World (Figure 1.12)

1. Members of the microbial world consist of two major cell types: the simple prokaryotic and the complex eukaryotic.

2. All organisms fall into one of three domains, based on the chemical composition and cell structure. These are the Bacteria, the Archaea, and the Eucarya. (Table 1.2)

The Bacteria (Figure 1.5)

1. The Bacteria are single-celled prokaryotes that have peptidoglycan in their cell wall.

The Archaea

1. Archaea are single-celled prokaryotes that are identical in appearance to the Bacteria. They do not have peptidoglycan in their cell walls and are unrelated to the Bacteria.

2. Many of the Archaea grow in extreme environments such as hot springs and salt flats.

The Eucarya

1. Eucarya have eukaryotic cell structures and may be single-celled or multicellular.

2. Microbial members of the Eucarya are the algae, fungi, and protozoa.

3. Algae can be single-celled or multicellular, and they can use sunlight as a source of energy. (Figure 1.6 and Table 1.3)

4. Fungi are either single-celled yeasts or multicellular molds and mushrooms. They use organic compounds as food. (Figure 1.7 and Table 1.3)

5. Protozoa are single-celled organisms that are motile by a variety of means. They use organic compounds as food. (Figure 1.8 and Table 1.3)


1. Organisms are named according to a binomial system.

2. Each organism has a genus and a species name, written in italics.

1.4 Viruses, Viroids, and Prions

1. The non-living members of the microbial world are not composed of cells. They are considered obligate intracellular parasites and include viruses, viroids, and prions.

2. Viruses are a piece of nucleic acid surrounded by a protein coat. They can infect members of all three domains. (Figure 1.9 and Table 1.4)

3. Viroids are composed of a single, short RNA molecule. Thus far, they are only known to cause diseases in plants. (Figure 1.10 and Table 1.4)

Chapter 1 Humans and the Microbial World

4. Prions consist only of protein, without any nucleic acid. They 1.5 Size in the Microbial World

Sizes of m (Figure 1.13)

cause several different neurodegenerative diseases of humans

1. Sizes of members of the microbial world vary enormously, and animals. (Figure 1.11 and Table 1.4)

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